A conventional web-based search engine is a program that searches a database for specified keywords and returns a list of the results where the keywords were found. Although search engine is generally a class of data mining programs, search engines are often used to search for documents (or websites) on the World Wide Web and USENET newsgroups. Search engines are accessible over the Internet.
Typically, a search engine operates by sending out a spider to fetch as many documents as possible. Another program, called an indexer, then reads these documents and creates an index based on the words contained in each document. In response to a search query, the engine may present a web page having enumerated links to other sites and/or documents related to the query.
Although convenient for searching for relevant results related to a search topic or keywords, it is possible to receive query results from unsecured sources that contain software developed to harm a computer system, such as a virus or malware. An unsuspecting user then selecting a link having a virus located therein may infect his/her computer potentially causing damage to the computer data stored therein.